What is Itzï?

Itzï is a dynamic, fully distributed hydrologic and hydraulic model that simulates :

  • Hydrological processes like rainfall and infiltration
  • 2D surface flows on a regular raster grid using simplified shallow water equations.
  • 1D drainage flow via the SWMM model
  • Bi-directional coupling between the drainage and the surface.

GIS integration

Itzï is built upon the open-source GIS software GRASS. This simplifies the pre- and post-processing of data. Map export or re-sampling are not needed. Notably, to change the resolution or the extend of the computational domain, the user just need to change the GRASS computational region and the raster mask. Itzï will automatically uses the entry data at the resolution and extent set in GRASS region.

All entry data can be represented as raster time-series, allowing the uses of radar rainfall or varying friction coefficient. Those can use relative or absolute time reference. An absolute time reference is useful to model historical events.

For example, if you have the following country-wide data:

  • Elevation at a resolution of 5m
  • Friction map at a resolution of 30m
  • 10 years of radar rainfall records at a resolution of 100m

It is very easy to model only one event of a specific watershed. You just need to:

  • Adjust the GRASS computational region to the extent and resolution needed
  • optionally, set a raster mask to finely delimit the catchment.
  • Set the Itzï’s configuration file with start and end dates of the event.

Surface–drainage coupled modelling

Itzï integrates the SWMM model with a partial inertia surface model. The interactions between the surface flows model and the drainage network model are done at the node of the drainage network by a set of weir and orifice equations, depending on the relative water depths in each model. The two models are run simultaneously and the exchange between the two are bi-directionals. The water can enter or exit the drainage network.

Hydrologic and hydraulic processes

Itzï comes with a hydrology module that manage direct infiltration, rainfall and lump sum losses. The infiltration can be represented by either a user-defined amount or estimated using the Green–Ampt formula.

The surface hydraulic processes are represented by two models:

  • A damped partial inertia model, based on a simplification of Saint-Venant Equations
  • A rain routing model that manage the flows under a given threshold

Open source

Itzï is released under the GNU GPL license. It is free to use for any purposes.

If you find Itzï useful and want to participate, great! There are different ways to help. Please find more details in the CONTRIBUTING.md document in the repository.